I just bought 3 digital manometers to digitalize my flow bench. I was wondering if anyone played around with digital manometers in lieu of a standard leak down test. For instance pressurizing the cylinder at a set amount and then looking at pressure differentials at the intake, exhaust, and breather. If nothing else the data obtained would not be variable on the size of the orafice between the gauges.
Leak down thoughts, manometers.
- Thread starter Chipg56
- Start date
Yes, that is one thing I was going to try. Just wondering if any one tried it as a substitute/enhancement for a leak down.
We solved many troubling problems with the blow by gauge.
OK here's a trouble shooting problem for y'all.
We had a real good old Red WKA flathead that had made it to .035 over and we only ran it in special races. Jimmy Glenn has teched this one more than once. So it had been sitting for a year, had 300 laps on it. I was checking it over before going to an important race.
Warmed it up and made a few full pulls on the dyno. She was down about .6HP full pull average and a half HP max.
BLOW BY WAS RIGHT WHERE IT SHOULD BE !
Leaked checked <1%,, Checked out the carb on the flow bench,, perfect. Cam timing spot on, valve springs perfect. Fresh fuel & oil, timing solid, same exhaust pipe this engine liked.For all practical purposes the engine was healthy. Checked calibration on the L&S Dyno, right on. Used weather correction, NO external issues in the shop.
SO ? What do you think we found to be wrong with the engine ??
WP
OK here's a trouble shooting problem for y'all.
We had a real good old Red WKA flathead that had made it to .035 over and we only ran it in special races. Jimmy Glenn has teched this one more than once. So it had been sitting for a year, had 300 laps on it. I was checking it over before going to an important race.
Warmed it up and made a few full pulls on the dyno. She was down about .6HP full pull average and a half HP max.
BLOW BY WAS RIGHT WHERE IT SHOULD BE !
Leaked checked <1%,, Checked out the carb on the flow bench,, perfect. Cam timing spot on, valve springs perfect. Fresh fuel & oil, timing solid, same exhaust pipe this engine liked.For all practical purposes the engine was healthy. Checked calibration on the L&S Dyno, right on. Used weather correction, NO external issues in the shop.
SO ? What do you think we found to be wrong with the engine ??
WP
Please let us know. the suspense is too great.
combative hodaka
Member
Less than 1% is more than remarkable with that amount of time on it (or any amount) is your leakdown in need of calibration? check again with a differant gauge.
racinnut15xm
Member
Valve job rusted? Sealed back up after being beat on the dyno?
Valve springs?
That's an interesting theory that makes since.
Well it's good to see from the answers that many of you have experience dyno testing engines.
OK,, we measured; RPM,,CHT,,EGT,,Crankcase Blowby,,Pressure tested the combustion space,, measured Torque and calculated HP.
I didn't have a way to measure intake vacuum !
The top piston ring is sealed against the cylinder wall by compression pressure behind it.
What seals this ring on the intake stroke ?? Radial ring tension to a large degree !
We installed a new well prepared ground and lapped top ring and the power returned just like it had always been.
So much is written about "Low Tension" rings,, but the consideration of how the engine draws in the precious fuel and air mixture is never mentioned along with this subject.
A leak down test that shows 3% under pressure will be much more under vacuum. And yes 1% leak down is accomplished with much attention to the cylinder, rings (OD and Face Angle) and piston ring land preparation. 1% is just about what a .003" ring gap will leak,, 300 laps??, well maybe .005". This was an unrestricted class engine, but the more the intake is restricted the greater the top ring tension should be, within reason of course.
There you have it, Best, WP
OK,, we measured; RPM,,CHT,,EGT,,Crankcase Blowby,,Pressure tested the combustion space,, measured Torque and calculated HP.
I didn't have a way to measure intake vacuum !
The top piston ring is sealed against the cylinder wall by compression pressure behind it.
What seals this ring on the intake stroke ?? Radial ring tension to a large degree !
We installed a new well prepared ground and lapped top ring and the power returned just like it had always been.
So much is written about "Low Tension" rings,, but the consideration of how the engine draws in the precious fuel and air mixture is never mentioned along with this subject.
A leak down test that shows 3% under pressure will be much more under vacuum. And yes 1% leak down is accomplished with much attention to the cylinder, rings (OD and Face Angle) and piston ring land preparation. 1% is just about what a .003" ring gap will leak,, 300 laps??, well maybe .005". This was an unrestricted class engine, but the more the intake is restricted the greater the top ring tension should be, within reason of course.
There you have it, Best, WP
Your post is intriguing. Wouldn't be very difficult to do a reverse leak down by introducing vacuum through the breather and measuring the differentials at the spark plug, intake, exhaust ports. By introducing the vacuum through a oil fill plug the breather could be checked. Not difficult but certainly more time consuming. For years I have been testing animal heads on the bench before ever mounting to the motor. I
On another related subject we all often talk about leak down gauges and percentages but rarely talk about the construction of the tool itself. I constructed mine with a few brass fittings and some relatively inexpensive gauges. Between the gauges there needs to be a restriction of air flow. The smaller the restriction, the more sensitive the tool will be. When constructed, I tried, using flathead jets as restrictions. Started with .060 and ended up using a stock gas jet. When using this tool 0-2% and the leak is not audible. 5-10% is clearly audible. It seems I never see any readings between 10 and 50%. My long winded point is if you are using a gauge commercially made for a car engine the restriction is probably too large to see small variations in a kart engine. I am curious, for those that know their gauges, what size of a restriction you find most valuable?
On another related subject we all often talk about leak down gauges and percentages but rarely talk about the construction of the tool itself. I constructed mine with a few brass fittings and some relatively inexpensive gauges. Between the gauges there needs to be a restriction of air flow. The smaller the restriction, the more sensitive the tool will be. When constructed, I tried, using flathead jets as restrictions. Started with .060 and ended up using a stock gas jet. When using this tool 0-2% and the leak is not audible. 5-10% is clearly audible. It seems I never see any readings between 10 and 50%. My long winded point is if you are using a gauge commercially made for a car engine the restriction is probably too large to see small variations in a kart engine. I am curious, for those that know their gauges, what size of a restriction you find most valuable?
You'll draw a vacuum from the spark plug hole to simulate the pressure drop during the intake phase. Also to get information you can use the engine needs to be hot with only the oil that's left in the cylinder after running.
I modified / fine tuned, my commercial gauge over 30 years ago but if memory serves me the orifice I use on small engines is .030 and test at 100 PSI.
WP
I modified / fine tuned, my commercial gauge over 30 years ago but if memory serves me the orifice I use on small engines is .030 and test at 100 PSI.
WP
I understand what you mean by lapped rings. its the grinding process i dont understand. could you shed some light on it?